An elevator typically comprises a hoistway, and an elevator car and a counterweight movable in the hoistway. The elevator further comprises a rotatable traction member, such as a traction wheel, engaging ropes connected to the car. The ropes pass around the rotatable traction member and suspend at least the elevator car and the counterweight. For controlling rotation of the rotatable traction member, the elevator comprises a drive machinery, which typically comprises a motor for rotating the rotatable traction member, a control unit for controlling the motor, as well as a brake for braking rotation of said rotatable traction member. Force for moving the car and counterweight is transmitted from the motor to the car via the rotatable traction member and the roping, whereby car movement can be controlled by controlling rotation of the rotatable traction member. The elevator comprises plurality of landings at which the elevator car is arranged to stop during use of the elevator for loading and/or unloading of the car.
In an elevator having traditional steel ropes, the ropes pass inside grooves of the rotatable traction member. In this kind of elevator the rope shape keep the tensioned ropes in their grooves. There are, however, elevators where the ropes cannot be reliably and gently guided by such grooves. This kind of challenges are mostly faced with belt like ropes. Particularly, “groove” type guidance, which includes considerable edges, cannot be used with ropes having sensitive surface structure and/or internal structure.
Running of a rope outside its intended course is potential to cause different dangerous problems such as damaging the rope itself or other components of the elevator. Thus, there is a need to prevent the rope from running outside its intended course, or in some other way prevent the situation from developing this far. This is challenging especially with solutions where the guidance by the rotatable traction member is not strong, such as with solutions where belt-like ropes are guided by cambered circumference of the rotatable traction member.
In solutions utilizing cambered (cambered shape also later referred to as crowning shape) traction member, it may happen that the rope reaches the shallow edge area between adjacent crowning shapes meant to guide adjacent ropes. Crowning acts as guidance of the rope and generally the total width of the crowning is the area where rope can move sideways. The intended placement of the rope is in the middle of the cambered area; but normally the rope is allowed to move sideways a little bit. Once a rope meets the shallow edge area it will try to climb along the cambered shape meant for the rope next to this rope. This is dangerous, firstly because the edge area will potentially damage the individual rope, but also because the rope configuration has changed away from how it is meant to be, which could cause dramatic system level problems.
A drawback of the known elevators has been that running of a rope outside its intended course, and further development of the problem into even more hazardous state have not been prevented in an adequately reliable manner. This has been a problem especially with elevators where mechanical shape-locking of the rope into its groove has been unreliable or impossible due to specific configuration of the ropes and the traction member.